This invention relates to electrical signal processing.
Where a digital memory is used to record a varying function, such as, for example, a time varying function, which is to be represented for viewing, such as by being displayed on a cathode ray tube, the independent variable, such as x or time t, is usually sampled at fixed and predetermined intervals so that it is not necessary to record the values of the independent variable x or t. These values are normally generated artificially at the time of readout by any suitable means, such as a counter or linear ramp. By noting the rate at which the values along the other coordinate, such as y-values, were sampled and recorded and also the sequence in which they were stored, it is normally quite easy to reassign an x or t-value to each y-value as it is read out.
This procedure eliminates the necessity to have an additional memory for the x or t-values and would appear to be a very efficient way of recording a function. However, this is only true provided at least 50% of the y-values which are recorded represent non-redundant information, namely y-values which cannot be estimated from the surrounding y-values, such as by a process of interpolation. If more than 50% of the y-values recorded are redundant, it would be more advantageous to use half of the memory for storing the x or t-values instead of recording at fixed intervals, and only recording so-called non-redundant y-values with their corresponding x or t-values, since the only purpose served by redundant values when recording at fixed intervals is to indicate the time relation or interval along the x-axis between two non-redundant y-values.
This can be a very inefficient way of storing this interval and it is accordingly an object of the present invention to provide an improved memory system which is only updated when non-redundant information presents itself.